斑块状沙化草甸周围气流流场特性的数值风洞实验

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Abstract In order to explore the mechanism of wind-sand erosion under the condition of patchy meadow underlying surface in desertified grassland, here in this paper, the meadow is generalized as porous medium for geometric modeling and the turbulence model is improved by additional porosity source terms in order to accurately characterize the interference effects of meadow on incoming air flow. Subsequently, based on the meadow coverage condition in the field test of Hesp (2019), the Standard k-ε, RNG k-ε and Realizable k-ε models are validated and optimized to achieve the model improvement. By referring to the wind speed near the ground (at 2m height) in the Maqu section of the Upper Yellow River, the numerical wind tunnel experiments of flow field characteristics around a single patchy meadow (1m×1m) were carried out under the conditions of meadow coverage of 15.75% (sparse), 31.05% (moderate) and 60.15% (dense) and forward threshold wind speed of 7m/s(low), 11m/s (medium) and 15m/s (high). The results show that a semi-circular low-speed zone on the windward side and a semi-elliptical shelter zone on the leeward side occur generally in the horizontal direction surrounding the meadow, the latter of which expands radially along the wind and accelerates in part on both sides. Moreover, for the vertical direction, the wind speed distribution generally shows the law of weakening on the windward side, sudden acceleration directly above, and large-scale deceleration on the leeward side. When the coverage is constant, the average wind speed around the meadow increases corresponding to the increase of the incoming wind speed. When the incoming wind speed remains constant and the coverage increases, the average wind speed on the leeward side of the meadow increases first and then decreases. The wind speed distribution around the meadow conform to the law of normal distribution, with a high narrow peak on the windward side and a low broad peak on the leeward side. The wind speed profile on the windward side can be fitted as the variogram of the Gaussian model, and the wind speed variogram on the leeward side closely relates to the incoming wind speed and coverage. The improved RNG k-ε turbulence model proposed in this paper can be used as a mathematical model to accurately characterize the complex air flow around the flexible meadow, which is also expected to provide a theoretical foundation for further numerical simulation of the wind-sand flow field for medium and large scale meadows.

Key words： grassland desertification patchy meadow porosity source air flow characteristics numerical wind tunnel

Received: 11 April 2023

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	WANG Zhi-jun
	ZHANG Kai-he

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WANG Zhi-jun,ZHANG Kai-he. Numerical wind tunnel experiment on surrounding air flow field characteristics of the desertified patchy meadow[J]. CHINA ENVIRONMENTAL SCIENCECE, 2023, 43(11): 5687-5699.

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http://www.zghjkx.com.cn/EN/ OR http://www.zghjkx.com.cn/EN/Y2023/V43/I11/5687

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